1. Field of the Invention
The present invention applies to radio communications systems in which several remote terminals communicate voice or data with several different base stations and, in particular, to such a system in which a remote terminal selects one from among a plurality of different base stations to begin a communications session.
2. Description of the Prior Art
Mobile radio communications systems such as cellular voice radio systems typically have several base stations in different locations available for use by mobile remote terminals, such as cellular telephones or wireless web devices. Each base station typically is assigned a set of frequencies or channels to use for communications with the remote terminals. The channels are different from those of neighboring base stations in order to avoid interference between neighboring base stations. As a result, the remote terminals can easily distinguish the transmissions received from one base station from the signals received from another. In addition, each base station can act independently in allocating and using the channel resources assigned to it.
Such radio communications systems typically include a broadcast channel (BCH). The BCH is broadcast to all remote terminals whether they are registered on the network or not and informs the remote terminals about the network. In order to access the network, a remote terminal normally tunes to and listens to the BCH before accessing the network. A remote terminal will typically scan a range of likely frequencies when it wants to access the network until it finds the strongest BCH, it will then use the information in the BCH to request access to the network. Such a request typically results in an exchange of information about the network using separate control and access channels and ends in the remote terminal receiving an assignment to a particular base station.
When a remote terminal moves to another location or when traffic load changes, the system may handover or hand-off the remote terminal""s assignment to another base station. In some systems, this assignment is done using information obtained from the remote terminal, for example in systems with MAHO (mobile assisted hand-off). In any event, central control requires resources at a central network control facility and the selections are primarily based on indirect information about the remote terminal. Such central control increases the complexity of the network and requires that more of the communications channel capacity be dedicated to base station selection and handover activity.
The present invention allows remote terminals to select from among many base stations without consuming significant overhead channel resources. This allows for better base station selections using almost no central network resources and almost none of the communications channel resources.
In one embodiment, the present invention comprises receiving a first broadcast burst from a first base station of a radio communications system, the first broadcast message including a first broadcast information sequence representing the power with which the first broadcast burst was transmitted, and measuring the received signal strength of the first broadcast burst. The invention further comprises receiving a second broadcast burst from a second base station of the radio communications system, the second broadcast burst including a second broadcast information sequence representing the power with which the second broadcast burst was transmitted, and measuring the received signal strength of the second broadcast burst. The invention further includes selecting a base station of the radio communications system for communication of data based on the first and second broadcast information sequence and the received signal strength of the first and second broadcast bursts.